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Biomedical subjects

T H Shaffer

Publications and source records attributed to T H Shaffer.

At least 127 records · Page 7Linked to original sources
PubMed1984

Liquid ventilation: effects on pulmonary function in distressed meconium-stained lambs.

Seven lambs (0.93 term gestation) were delivered by cesarean section with evidence of meconium in the amniotic fluid, meconium staining, and respiratory distress. The initial arterial blood gas and acid-base status indicated severe hypoxemia and acidosis. Three of these lambs developed pneumothoraces and died on control gas ventilation with positive end expiratory pressure. During the control period (90 min) with ventilatory support, there were no significant alterations in mean arterial oxygen tension (PaO2) and alveolar-arterial oxygen gradient (A-aDO2). The initial hypercarbia and acidosis were effectively controlled and corrected using mechanical ventilation and bicarbonate infusion. Fifteen min after the onset of fluorocarbon ventilation mean PaO2 significantly increased and A-aDo2 decreased. After 90 min of fluorocarbon ventilation, lambs were returned to gas ventilation. During this recovery period, PaO2 and A-aDo2 remained significantly improved compared with control gas values. Dynamic lung compliance increased, alveolar and peak tracheal pressure decreased and inspiratory elastic work of breathing decreased during liquid ventilation.

Animals↗
PubMed1984

Physiological effects of ventilation with liquid fluorocarbon at controlled temperatures.

Body cooling, respiratory heat loss, and the physiological effects of liquid ventilation at various temperatures were studied in 10 adult cats with applications to the deep sea diver. The animals were stabilized on mechanical gas ventilation with 100% oxygen during a control period and then mechanically ventilated for 1 h with liquid fluorocarbon. Fluorocarbon (Rimar 101) temperatures of 10 degrees C, 20 degrees C, and 30 degrees C were used to ventilate the animals while rectal and subcutaneous body temperatures were being measured. For the 3 temperature conditions, respective cooling rates of 9.0 degrees C/h, 7.8 degrees C/h, and 3.6 degrees C/h, as well as respiratory heat losses of 65,637 J X kg-1 X h-1, 33,488 J X kg-1, X h-1, 18,036 J X kg-1 X h-1 were observed while maintaining effective physiological gas exchange [mean PaO2 = 353 +/- 28 (SEM) mmHg, mean PaCO2 = 30 +/- 2 (SEM) mmHg]. Changes in cardiovascular variables were noted as mild (35 degrees C-30 degrees C) and moderate (30 degrees C-25 degrees C) levels of hypothermia were reached. Cardiac output, oxygen consumption, heart rate, and mean blood pressure were significantly correlated with rectal temperature. The data presented herein quantitate the effects of liquid ventilation on body cooling and respiratory heat loss. Furthermore, the physiological alterations associated with the observed hypothermic condition could severely limit the effectiveness of a human diver if not carefully controlled.

Animals↗
PubMed1983

Effect of liquid ventilation on preterm lamb tracheal mechanics.

Liquid ventilation with fluorocarbon has been demonstrated as a viable mode of ventilatory support to preterm or distressed lambs. The effect of liquid ventilation and its high inflation pressures in proximal airways was evaluated on the mechanical behavior of the preterm trachea. 7 preterm lambs (134 +/- 1.5 SE days of gestation; 90% term) were ventilated with fluorocarbon (Rimar) for 58.6 +/- 8 min. The tracheae were dissected and the ventilated, distal segments were compared to nonventilated proximal segments. Pressure-volume curves were determined by plethysmography and specific tracheal compliance was computed. Tracheal dimensions increased 13.6 and 25.6% in diameter and volume (p less than 0.05), respectively, and the compliance decreased 29.9% (p less than 0.05). The magnitude of these changes is comparable to that observed during gaseous ventilation of term animals.

Animals↗
PubMed1983

The effects of liquid ventilation on cardiopulmonary function in preterm lambs.

The effects of fluorocarbon ventilation on cardiopulmonary function were studied in 8 preterm lambs, 132-136 days gestation. After mechanical ventilation with 100% oxygen (control period), the lambs were ventilated with fluorocarbon (PIO2 = 622 torr). The liquid was then removed from their lungs and gas ventilation resumed (recovery period). During normothermic liquid breathing the alveolar-arterial O2 gradient (A-a DO2) decreased (P less than 0.01) from control by 154 torr and remained decreased (P less than 0.05) by 85 torr during recovery. Dynamic lung compliance (CL) increased 50% (P less than 0.05); PaO2 increased 50% (P less than 0.05); and PaCO2 decreased 29% (P less than 0.01) as compared to control values. The change in A-a DO2 and PaO2 before and after liquid ventilation was correlated (r = 0.79 and P less than 0.01) with control CL. There was a gradual decrease (P less than 0.01) in mean arterial pressure from 62 +/- 5.4 torr (control) to 53,1 +/- 9,3 torr (recovery); however, there were no significant alterations in mean central venous pressure, heart rate, or mean electrical axis.

Animals↗
PubMed1983

Cardiopulmonary function in very preterm lambs during liquid ventilation.

Cardiopulmonary function was evaluated in very preterm lambs (106 +/- 0.7 S.E. days gestation, 1.66 +/- 0.12 S.E. kg birth weight) during fluorocarbon ventilation. Lambs were delivered by cesarean section after epidural anesthesia. Indwelling arterial, venous, and tracheal cannulae were placed before clamping the cord. Lambs were then mechanically ventilated with oxygenated fluorocarbon for approximately 2 h. During this period it was possible to maintain adequate gas exchange and stable cardiac function. Transpulmonary pressure, liquid flow, and tidal volume tracings enabled determination of lung compliance, CL = 0.58 +/- 0.12 S.E. ml X cmH2O-1 X kg-1, inspiratory resistance, RI = 3600 +/- 604 S.E. cmH2O X liter-1 X sec-1, and expiratory resistance, RE = 4034 +/- 2183 S.E. cmH2O/liter/sec. Lung compliance of the 106-day-old fluorocarbon-filled lung is similar to the more mature 138-143-day-old air-filled lung in preterm lambs. Based on the data presented herein we have extended the viability of the preterm lamb to the limit of pulmonary capillary development rather than that of the pulmonary surfactant system.

Acid-Base Equilibrium↗
PubMed1983

Decompression incidence in air- and liquid-breathing hamsters.

The effects of hyperbaric compression on heart rate, rectal temperature, respiratory rate, bubble formation, and survival were studied in three groups of anesthetized golden hamsters (Mesocricetus auratus). Group I (15 animals) breathed air while exposed to 7 ATA of pressure for 1 h in a hyperbaric chamber; Group II (13 animals), at the same pressure level (7 ATA) and for the same time period (1 h), breathed an oxygenated fluorocarbon liquid (temperature 27 degrees C) that was open to the chamber atmosphere; Group III (10 animals), at the same pressure and time period as the other groups, were sealed in a flexible plastic bag filled with oxygenated fluorocarbon as a breathing mixture. A fourth, Group IV (12 animals), breathed oxygenated fluorocarbon for 1 h at 1 ATA. Survival after rapid decompression in each group varied, 9 animals died in Group I, 12 animals in Group II, whereas none of the animals died in either Groups III or IV. Thirty minutes after decompression postmortem examinations of all the animals demonstrated the presence of large amounts of gas bubbles in the right ventricle and some gas bubbles in the left ventricle of all the hamsters in Groups I and II. No gas bubbles were found in the hearts of the Group III animals. Group III animals, breathing a liquid unsaturated by an inert gas, survived rapid explosive decompression without the signs and symptoms of decompression sickness. Immersion in the liquid fluorocarbon produced a profound decrease in heart rate, rectal temperature, and respiration in Groups II, III, and IV.

Air↗
PubMed1982

Time-dependent tracheal deformation in fetal, neonatal, and adult rabbits.

Sequential magnitude and the rate of change in tracheal mechanics after application of intermittent positive pressure (IPP), and the time constant, tau, of this deformation were determined in fetal (21 and 27 days gestation), neonatal (term, 31 days gestation) and adult rabbits. In vitro tracheal mechanics were determined by liquid plethysmography before and after IPP, (25 cm H2O at 30 cycles/min) of 20, 40, 60, and 120 min duration. A sequential decrease in tracheal compliance was documented at all ages. This was associated with increased values of tau as the maturational age advanced. Further, the rate of tracheal deformation was 0.008 cm H2O min-1 at 21 days gestation compared to 0.00025 cm H2O min-1 at adulthood. The decrease in rate of deformation was related to the gestational maturity and duration of IPP. The rate of deformation, as predicted by calculated deformation time constants, appears to be a function of structural elastic and viscoelastic properties of the trachea as well as the duration and magnitude of applied pressure. The deformation time constant may be defined as a useful index to predict the rate of airway deformation. Utilizing the rabbit model, this provides a measure of comparing barotrauma with different modes of ventilation in preterms.

Age Factors↗
PubMed1981

Pressure--volume relationships of tracheae in fetal newborn and adult rabbits.

The physical properties of the trachea in fetal, newborn, and adult rabbits change with age. Tracheal dimensions and pressure--volume relationships were determined in excised tracheae at a wide developmental age range (from early gestational age to infancy and adulthood). At intraluminal pressures of 0 to 10 cm H2O, the tracheal specific compliance was 0.089 (cm H2O)(-1) for a 21 day old fetus. By adulthood, the tracheal specific compliance decreased five fold to 0.017 (cm H2O)(-1); a dramatic proportion of this reduction occurred during fetal life itself, followed by a steady, progressive decline to adult age. The volume of the tracheal segment, at intraluminal pressure of 20 cm H2O, increased by 29% (adult), 41.5% (31 day fetus) and 113% (21 day fetus). Developmental alterations in the specific airway compliance suggest significant changes in anatomical dead space would occur as a function of maturation and airway transmural pressure.

Aging↗
PubMed1981

Respiratory muscle function, assessment, and training.

This article presents a brief overview of respiratory muscle mechanics and the effects of lung disease and neuromuscular disease on pulmonary function. A variety of current specific and general muscle training techniques are described and discussed. Also presented is a current review of training studies and the effects of muscle training on cardiopulmonary function, muscle strength, endurance and fatigue, and exercise tolerance.

Adult↗
PubMed1981

Successful extubation of neonates: clinical and physiological factors.

Arterial blood gases, pulmonary mechanics, lung volume measurements and clinical profiles were determined pre and postextubation in 19 infants recovering from respiratory disease. This study evaluated clinical and physiological factors which may be valuable in predicting successful extubation in neonates. Of the 19 patients, 4 required reintubation within 72 h. In this group of patients, the combined profile of low birth weight (1050 g), low gestational age (31 weeks), and high pulmonary resistance (inspiratory 278 cm H2O/L X sec, expiratory 309 cm H2O/L X sec) was significantly different from the 15 patients who were successfully extubated. In addition, lower pHa after extubation was also characteristic of those infants requiring reintubation.

Airway Resistance↗
PubMed1981

Use of external expiratory resistance in intubated neonates to increase lung volume.

Ten intubated neonates (weights 0.90 to 2.58 kg) recovering from respiratory disease had lung mechanics, respiratory patterns, and functional residual capacity measured at 0 cmH2O continuous positive airways pressure and then after application of serially increasing levels of external expiratory resistance. At an external expiratory resistance greater than 40 cmH2O/1 per second, there was a significant increase in mean functional residual capacity compared with control levels. Immediately after the application of external expiratory resistance, there was a significant decrease in flow which returned to control values after a few breaths. Tidal volume and respiratory rate decreased for a few breaths after the application of the external expiratory resistance, but returned to control values after several seconds. Study age, gestational age, or study weight had no appreciable effect on the relationship between functional residual capacity and external expiratory resistance. Application of external expiratory resistance may be useful for stabilising lung volume in neonates recovering from respiratory disease.

Humans↗
PubMed1981

Effect of intermittent positive pressure application on the bulk modulus of the developing rabbit trachea.

Tracheal dimension, pressure-volume relationships and bulk modulus (K) were determined in excised fetal and adult rabbit tracheal segments before and after application of intermittent positive pressure (IPP) which was 0--25 cm H2O pressure, at 30 cycles/min, and for a duration of 60 min. Both tracheal elastic behavior and dimensions underwent dramatic changes following IPP. At 21, 27, 31 days gestation age, the bulk modulus, K, of the rabbit trachea approximated those of the adult control values. However, the adult values of K did not vary significantly after IPP. The associated increase in tracheal dimensions were also related to the maturity of the animal. Significant structural and functional barotrauma is thus sustained by immature airways, and may account for the tracheal deformation frequently observed as a result of IPP.

Aging↗
PubMed1981

Instrumentation for measuring cardiac output by direct Fick method during liquid ventilation.

A closed-circuit fluorocarbon oxygenation system was designed and incorporated into an existing liquid breathing system (LBS) to allow measurement of an animal's oxygen consumption during liquid ventilation. This enabled simultaneous determination of cardiac output by the direct Fick method. A series of seven in-vivo experiments were conducted in which the oxygen consumption and cardiac output of adult cats (2.3 +/- 0.1 kg body wt SEM) were measured during both spontaneous gas breathing (Fio2 = 0.80 in the control animals) and fluorocarbon liquid (FC-80) ventilation using the LBS. On conversion to liquid ventilation, cardiac output and oxygen consumption were found to decrease significantly, by 40% (P less than 0.02) and 18.6% (P less than 0.05), respectively, from control values for gas breathing. Use of the closed-loop fluorocarbon oxygenation system provided for total recovery of vaporized fluorocarbon (greater than 750 ml/h) and of oxygen (18 liter/min STPD), which were otherwise discarded in previous experiments with liquid ventilation.

Animals↗
PubMed1981

Pressure-induced deformation in immature airways.

The effect of positive pressure ventilation on the highly compliant fetal airways was evaluated utilizing fetal rabbit tracheal segments. The degree of mechanical and dimensional deformation was quantified to the pressure applied intermittently (IPP) or continuously (CPAP) for 60 min. Excised tracheal segments were obtained at 21, 27, and 31 days fetal rabbit gestation (term = 31 days) and from 18 +/- 6-month-old adults. Internal diameter, resting length, and volume of the tracheal segments were measured, and their pressure-volume relationships were determined by plethysmography. Tracheal specific compliance at deflation pressure of 0 to 10 cm H2O was calculated from these data. In all fetal groups, the application of positive pressure resulted in a decrease of both tracheal distensibility and the slope of the pressure-volume curves; in addition, a highly significant decrease in tracheal specific compliance was documented. At 21 days gestation, the tracheal specific compliance decreased from 0.089 to 0.034 cm H20-1 (P less than 0.001) after CPAP and to 0.025 cm H2O (P less than 0.001) after IPP. For the same group, the resting tracheal volume increased by a dramatic 89% (P less than 0.001) after CPAP and by 124% (P less than 0.001) after IPP. The magnitude of these alterations decreased as gestational age advanced; the changes were not significant by adulthood. These data indicate that significant pressure-induced deformation (barotrauma) is sustained by susceptible immature airways.

Animals↗
PubMed1981

Increased pulmonary vascular resistance during liquid ventilation.

The effect of liquid ventilation on pulmonary vascular resistance was studied in an isolated cat lung preparation in situ. Lungs were perfused with whole blood from a donor cat at a constant flow of 100 ml . min-1 kg-1. Pulmonary arterial venous pressures were measured, and pulmonary vascular resistance calculated during gas ventilation (control) and ventilation with fluorocarbon, FC-80. During control ventilation at a mean tidal volume (VT) of 28 +/- 1 (SEM) ml and lung volume of 108 +/- 8 (SEM) ml, pulmonary vascular resistance was 0.07 +/- 0.01 (SEM) PRU. During liquid ventilation at similar lung volumes, pulmonary vascular resistance increased by 62% to 0.12 +/- 0.03 (SEM) PRU (P less than 0.05). At greater liquid lung volumes reflecting optimum CO2 elimination, pulmonary vascular resistance increased by 115% over control values to 0.15 +/- 0.01 (SEM) PRU (P less than 0.005). These data demonstrate significant alterations in pulmonary circulation during liquid ventilation, and suggest that further studies should be completed before hyperbaric applications in human can be considered.

Animals↗
PubMed1980

The effect of external expiratory resistance on lung volume and pulmonary function in the neonate.

To investigate the acute physiologic effects of external expiratory resistance on lung function in extubated neonates recovering from respiratory disease, lung mechanics, respiratory patterns, and functional residual capacity were measured in ten neonates dueing a control period and immediately after application of an external expiratory resistance of 30 cm H2O/l/second via a face mask. Following application of EER, mean FRC increased by 40.8% (P less than 0.05). The work of breathing was significantly increased after the EER was applied; there was also a significant increase in measured expiratory resistance and a decrease in inspiratory-expiratory time ratio. The change in lung volume was rapid, requiring less than five seconds for the new end-expiratory level to be reached. Dynamic lung compliance, inspiratory resistance, and respiratory rate did not change during any phase of the study. The application of external expiratory resistance may have potential therapeutic value by increasing lung volume in infants recovering from respiratory disease.

Airway Resistance↗